Since cardiomyocytes lose their division potential at the time of birth and hence their regeneration is difficult, recent interest has focused on replacement therapy wherein cardiomyocytes obtained by inducing differentiation of cells having pluripotency (Patent Document 1), such as embryonic stem cells (ES cells) or induced pluripotent stem cells (iPS cells), are transplanted to a cardiac tissue damaged due to myocardial infarction, myocarditis, aging or the like. Although many methods for inducing differentiation of such pluripotent stem cells into cardiomyocytes have been reported (Patent Document 2, Patent Document 3, Non-patent Document 1, Non-patent Document 2, and Non-patent Document 3), their efficiencies of differentiation induction into cardiac muscle are insufficient for clinical application.